MONITORING LY-ALPHA EMISSION FROM THE BLAZAR 3C-279

The blazar 3C 279 is well studied and shows frequent large continuum f lares from radio to gamma-ray wavelengths. There have been a number of multiwavelength observations of 3C 279, and hence there are extensive ultraviolet data for this object available in the UV archives. In thi s paper we present Ly alpha emission line measurements for 3C 279 usin g all the archival IUE SWP spectra from 1988 to 1996 and all archival Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) G190H spe ctra from 1992 to 1996. Individual archival IUE spectra of 3C 279 show weak Ly alpha emission at similar to 1868 Angstrom (z = 0.536), which is easily seen in the co-added data. The Ly alpha emission is observe d in all the HST/FOS spectra. The strength of Ly alpha is nearly const ant (similar to 5 x 10(-14) ergs cm(-2) s(-1)), while the 1750 Angstro m continuum varies by a factor of similar to 50, from similar to 0.6 t o 31.6 x 10(-15) ergs cm(-2) s(-1) Angstrom(-1). The behavior of the L y alpha emission line flux and continuum flux is similar to that of th e only other well observed blazar, 3C 273, which shows constant line f lux while the continuum varies by a factor of similar to 3. This near- constancy of emission-line flux in the two best-studied blazars sugges ts that the highly variable beamed continuum is not a significant sour ce of photoionization for the gas. Some other source, such as thermal emission from an accretion disk, must be providing a significant fract ion of the photoionizing flux in these objects. The large amplitude va riability seen at gamma-ray energies must be due to changes in the ene rgetic electrons in the jet rather than changes in the external photon field.